The present invention relates to an electromagnetic solenoid and to a shift actuator for a transmission using the electromagnetic solenoid for actuating, in a direction of shift, a shift lever to operate a gear-changing mechanism of the transmission mounted on a vehicle.
As a shift actuator for a transmission for actuating, in the direction of shift, a shift lever to operate the gear-changing mechanism of the transmission, there has generally been used a fluid pressure cylinder using, as a source of operation, a pneumatic pressure or a fluid pressure such as hydraulic pressure or the like. The shift actuator using the hydraulic cylinder requires a piping for connection to the source of fluid pressure, an electromagnetic change-over valve for changing over the flow passage of the operation fluid, and requires space for their arrangement. These requirements are accompanied by a problem of an increase in the weight of the apparatus as a whole.
In recent years, further, there has been proposed an actuator driven by an electric motor as a shift actuator for a transmission mounted on a vehicle that is equipped with neither a source of the compressed air nor a source of hydraulic pressure. Unlike the actuator that uses a fluid pressure cylinder, the shift actuator constituted by an electric motor requires none of the piping for connection to the source of fluid pressure or the electromagnetic change-over valve. Therefore, the device as a whole can be constituted in a compact size and in a light weight. However, the actuator driven by the electric motor requires a reduction mechanism for obtaining a predetermined operation force. As reduction mechanisms, there have been proposed the one that uses a ball-screw mechanism and the one that uses a gear mechanism. The actuators using the ball-screw mechanism and the gear mechanism, however, are not necessarily satisfactory in regard to durability of the ball-screw mechanism and the gear mechanism, in regard to durability of the electric motor and in regard to the operation speed.
Meanwhile, JP-A 2002-213606 discloses a shift actuator for a transmission that uses an electromagnetic solenoid, as an actuator that has excellent durability and a high operation speed.
It is necessary that the shift actuator for a transmission must come to a halt at a neutral position of the gear-changing mechanism. Due to its structure, however, the electromagnetic solenoid is actuated to a position where the electromagnetic coil is excited and to a position where the electromagnetic coil is not excited, but comes, with a great difficulty, to a halt at the intermediate position. To halt the electromagnetic solenoid at the intermediate position, a position detection means and a complex control device including feedback control are necessary. Therefore, if the electromagnetic solenoid can be brought to a halt at the intermediate position without using the position detection means and the complex control device, its application to a variety of equipment can be expected.
It is a first object of the present invention to provide an electromagnetic solenoid that can be brought to a halt at the intermediate position without using a position detector means and a complex control device. It is a second object of the present invention to provide a shift actuator for a transmission using an electromagnetic solenoid that can be brought to a halt at the neutral position of the gear-changing mechanism without using a position detector means and a complex control device.
In order to achieve the above first object, the present invention provides an electromagnetic solenoid comprising a cylindrical body yoke, a front yoke arranged on one end side of the body yoke, a fixed yoke that is formed integrally with the front yoke and is arranged in the body yoke, a back yoke arranged on the other end side of the body yoke, an annular center yoke arranged at the central portion of the body yoke in the axial direction thereof, a first annular electromagnetic coil that is arranged along the inner peripheral surface of the body yoke between the center yoke and the front yoke so as to surround the fixed yoke, a second annular electromagnetic coil arranged along the inner peripheral surface of the body yoke between the center yoke and the back yoke, an operation rod arranged being inserted through the front yoke and the fixed yoke so as to move in the axial direction, a first moving yoke mounted on an end of the operation rod on the side of the back yoke, a second moving yoke arranged on the operation rod so as to slide between the first moving yoke and the fixed yoke, and a limiting means for limiting the second moving yoke from moving toward the back yoke at an intermediate position in a range in which the first moving yoke moves.
It is desired that a magnetism shut-off ring made of a non-magnetic material is provided in the central portion of the body yoke in the axial direction thereof. Further, the limiting means comprises a stopper portion which protrudes inward in the radial direction on the inner peripheral surface of the center yoke.
In order to achieve the above second object, further, the present invention provides a shift actuator of a transmission equipped with a first electromagnetic solenoid and a second electromagnetic solenoid for actuating, in the directions opposite to each other, an operation member coupled to a shift lever for operating a gear-changing mechanism of the transmission, wherein said first electromagnetic solenoid and said second electromagnetic solenoid comprise, respectively, a cylindrical body yoke, a front yoke arranged on one end side of the body yoke, a fixed yoke that is formed integrally with the front yoke and arranged in the body yoke, a back yoke arranged on the other end side of the body yoke, an annular center yoke arranged at the central portion of the body yoke in the axial direction thereof, a first annular electromagnetic coil that is arranged along the inner peripheral surface of the body yoke between the center yoke and the front yoke so as to surround the fixed yoke, a second annular electromagnetic coil arranged along the inner peripheral surface of the body yoke between the center yoke and the back yoke, an operation rod that is arranged being inserted through the front yoke and the fixed yoke so as to move in the axial direction and is coupled to the operation member, a first moving yoke mounted on an end of the operation rod on the side of the back yoke, a second moving yoke arranged on the operation rod so as to slide between the first moving yoke and the fixed yoke, and a limiting means for limiting the second moving yoke from moving toward the back yoke at an intermediate position in a range in which the first moving yoke moves.